Railway track circuits



Patented Apr. 1, 1952 RAILWAY TRACK omoUrrs Paul N. Martin,

Penn Township,

Allegheny County, Pa., assignor to Westinghouse Air Brake Company, a corporation of Pennsylvania Original application July 18, 1944, Serial No. 545,519. Divided and this application April 30, 1946, Serial No. 665,944

My invention relates to railway track circuits,

'and more particularly to track circuits using vacuum tubes for track relays.

The present application is a division of my copending application, Serial No. 545,519, filed July 18, 1944, for Vacuum Tube Circuits, now Patent Number 2,541,879, dated February 13, 1951.

When a vacuum tube and particularly a gas tube is used as a relay for a railway track circuit, the bias voltage used to control the conductive condition of the tube must be checked because the loss of a bias voltage might result in the tube being made conductive corresponding to the unoccupied condition of the track circuit when the section is occupied.

Accordingly, a feature of my invention is the provision of track circuit apparatus incorporating novel and improved means to check the bias voltage of a gas tube used as a track relay and to assure proper phase relationship for the voltages of the different tube circuits.

Other features, objects and advantages embodying my invention will appear as the specification progresses.

va broken element of the bias circuit results in, a

loss of power for the anode circuit and the tube cannot be fired in response to such failure. The

control grid circuit includes means through which the phase relationship of the voltage applied to the control grid from the track rails can be preselected and thus proper phase relationship between the voltage of the control grid circuit and the voltages of the anode and shield. gridcircuits can be predetermined. In the presentapplication the shield grid and the control grid are at times referred toas control electrodes because both of the grids serve to control the operating characteristics of the tube.

I shall describe three forms of. track circuit apparatus embodying my invention, and shall then point out the novel features thereof in claims.

In the accompanying drawings, Fig. 1 is a diagrammatic view showing one form of railway track circuit embodying my invention when using a gas tube and an alternating current. Figs. 2 and 3 are diagrammatic views showing two dif- 3 Claims. (01. eta-e4) ferent forms of railway track circuits embodying my invention when using gas tubes and coded direct current. i

In each of the different views like reference characters are used to designate similar parts.

Referring to Fig. 1, the reference characters Ia and lb designate the track rails of a stretch of railway track formed by the usual insulated rail joints with a track section D-E, and which section may be one section of a series of sections of a signal system. Section D-E is provided with a track circuit comprising a source ,ofcurrent connected across the rails at one end of the section and a track relay connected across the rails at the opposite end of the section. The immediate source of current for the track circuit of section D-E is a track transformer TE, a primary winding 6 of which is connected to an alternating current transmission line including line wires LI and L2 connected to a generator, not shown. A secondary winding 1 of transformer TE is connected across the rails la and lb 2. current limiting impedance 8 being preferably interposed in the connection.

The track relay for section D-E comprises a tube VI and associated circuits. Tube VI may take different forms, and it is disclosed as an indirectly heated gas tetrode having an anode 9, a cathode In, a control grid II and a shield grid 12. Tube VI is provided with two terminals for the shield grid [2, each end of the grid l2 being connected to a terminal. Thus, a circuit connected to the two terminals of the shield grid includes the shield grid in series so that any break in the shield grid or its connections within the tube will interrupt the circuit. The filament of the tube VI is heated from a secondary winding I3 of a line transformer TL, a primary winding 14 of which transformer is connected across the transmission line.

Tube VI is provided with a control grid circuit receiving energy from the track rails through a track transformer TRD and a phase shifting impedance. Specifically, a primary winding-2 of transformer TRD is connected across the rails Ia and lb through wires 61 and 68, a resistor 69 being preferably connected in multiple with winding 2. Secondary winding 4 of transformer TRD is included in the control gridcircuit which extends from grid Ii through resistor I5 to the junction terminal of an adjustable inductance l6 and a resistor 5 connected in series across the outside terminals of winding 4, and from an incurrent supplied to the rails through track transformer 'I'E causes a voltage to be applied to the control grid II of tube VI, the phase of the voltage applied to the grid with respect to the phase of the voltage across the rails being predetermined through the inductance I6 and resistor 5. The resistor'69 is provided in order to limit the amount of phase shift with changes in ballast conditions, but such resistor may not be needed. Also, the bias battery II is provided to give a normal negative bias voltage, but such bias battery may not be required.

Shield grid or control electrode I2 is included in a biasing circuit that can be traced from the right-hand terminal of secondary winding I; of line transformer TL through wire I8, primary winding I9 of a transformer TP, wire 20, one terminal of the shield grid I2, the shield grid t2, the other terminal of the grid and wire 2I to the left-hand terminal of winding I'I. Wire I8 is connected to cathode ID of the tube through wire 25', and thus the shield grid I2 is ,of a potential with respect to cathode I9 proportional to the voltage of secondary winding H. An anode circuit for tube VI extends from the top terminal of secondary winding 22 of transformer TP through a battery I2, resistor 23, winding of a relay CR, Wire 24, plate 9 and intervening tube space to cathode Iil of tube VI and wires IQ and 25 to the other terminal of winding 22. It is to'be seen that secondary winding ll of the line transformer TL not only supplies abias voltage for the shield grid I2 with respect to cathode I but also supplies power through transformer TP to the anode circuit of the tube. Thus a loss of power at secondary winding Il' or a broken circuit element for the biasing circuit of shield grid I2 will result in a loss of power for the anode circuit of the tube.

Plus and minus signs have been placed on certain of the circuit elements of Fig. l to indicate the relative polarity of the parts during one half cycle of the voltage of the transmission line LI--L2, the relative polarity of these circuit parts being reversed from that indicated during the other half cycle of the voltage. During the half cycle, the voltage is that indicated'by the plus and minus signs, the shield grid I2 is negative in potential with respect to cathode I0 and the anode 9 is positive in potential with respect to the oathode. The parts are "so proportioned that the higher voltages of such half cycle applied to the anode are sufiicient to fire the tube, except for the negative bias effected through the shield grid I2. It is to be pointed out that battery I2 is of a voltage insuflicient to fire tube VI and serves to aid in preselecting the portion of the cycle of the alternating voltage'supplied through transformer TP the tube is conductive. The battery I2 may not be needed and may be omitted.

Normally, that is, when the track section DE is unoccupied, the control grid II is driven positive in potential with respect to cathode." I0 during the half cycle the anode 9 is positive and such positive bias voltage for the control grid II causes tube VI to be fired and relay CR. energized by the anode current During the followinghalf cycle of the voltage the anode 9 is negativewith respect to the cathode I0 and the tube is deionized. On the next positive half cycle the tube is fired again so that relay CR is energized by impulses of the anode current and its armature is retained picked up as long as such impulses of, current flow because of the slow release characteristic of the relay. It is to be observed that the proper phase relationship of the voltage applied to the control grid II is preselected by the adjustment of the inductance I6 and resistor 5.

When the track section DE is occupied, the control voltage impressed across control grid II and cathode It is shunted and the tube VI remains non-conductive because of the bias voltage applied to the shield grid I2.

It is apparent that in Fig. 1 there is disclosed ,a, track circuit using a gas tube as a track relay and through which tube a control relay CR is retained energized in response to the track section-being unoccupied, and is deenergized when the section is occupied. Furthermore, a loss of power at winding ll of the line transformer so that there is a loss of bias voltage for the shield grid I2 results in a loss of power for the anode circuit and the tube cannot be fired because of such failure. Also any broken circuit element for the shield grid circuit results in a loss, of power for the anode circuit and the tube cannot be fired because of such a broken circuit element. V

In Fig. 2, the rails Ia. and lb are formed with a track section DE the same as in Fig. 1 Section DE ofv Fig. 2 is provided with a track circuit, the source of power of which is a battery BE connected across the rails through a contact Ia of a code transmitter 'IBBCT. Code transmitter [800T may be of any one of the several constructions known to the art and it is suff cient for this application to point out that the coder I80CT is constructed to actuatea, contact merriber I801) to recurrently engage contact IBOa at a preselected code rate such as, for example, I80 times per minute, the arrangement being such that contact ISOa is closed substantially one-half of each code period. It follows that the track circuit current for section DE of Figl 2 is a coded direct current of a preselected code rate.

The track relay means responsive to the coded direct current of the track circuit of Fig. 2 includes gas tube VI and a code following relay CF together with associated circuits. The shield grid I2 of tube VI is included in a biasing circuit extending from the positive terminal of a battery 26, through resistor 21, winding of a check relay CC, resistor 28, one terminal of shield grid I2 to its other terminal and wire 29 to the negative terminal of battery 26. Cathode I0 of tube VI is connected through wire 30 to an intermediate terminal 3| of the resistor 28, and it is clear that shield grid I2 is madenegative in potential with respect to cathode II) by a voltage preselected by the position of the intermediate terminal 3I. Also the check relay CC, which is included in series with the shield grid I2 is energized and picked up by the current flowing in this circuit, but that any broken qnnection or circuit element of the circuit results in the deenergizing of the check relay.

An anode circuit for the tube VI of Fig. 2 can be traced from the positive terminal ofbattery 26, through resistor "21, front contact 92 of'th-e check relay CC, winding of code following relay CF, wire 33, anode 9 and tube space to" cathode I0 of the tube, wire 3 9 to intermediate terminal 3| of resistor 28 and thence through'the shield grid circuit to the negative terminal of battery 26. Thus the anode 9 is made positive in potential with respect to the cathode I9 when the shield grid circuit is complete so that the check relay CC is energized. The parts are so proportioned that the voltage applied to the anode 9 is sufficient to fire the tube except for the negative bias voltage applied tothe shield grid I 2. Tube VI of Fig. 2 is provided with a condenser Cl and a resistor 34 together with a shunt path by which the condenser Cl is connected across the anode 9 and cathode through a front contact 35 of the code following relay CF.

The control grid I I is connected across the rails of the section D-E through a circuit including resistors 69 and i as will be readily understood by an inspection of Fig. 2.

Normally, that is, when the track section D-E of Fig. 2 is unoccupied, a control voltage is applied to the control grid ll of tube VI each on period of the coded track circuit current due to the voltage drop across resistor 59, the control grid l I being driven in the positive direction with respect to the cathode ID. This control voltage applied to the control grid ll counteracts the negative bias voltage applied to shield grid i2 and the tube Vi is fired causing the code following relay CF to be energized and picked up by the current flowing through the anode circuit. Prior to the picking up of the relay CF, the condenser Cl is charged through resistor 34 and the 'tube, the right-hand terminal of condenser Cl as viewed in Fig. 2 being the positive terminal. With relay CF picked up to close front contact '35 condenser Cl is connected directly across the anode and cathode of the tube VI to deionize the tube with the result relay CF is deenergized and released. The parts are so proportioned that the "on period of the coded track circuit current is slightly less than the time required for the relay CF to be picked up and for condenser CI to deionize the tube. Consequently, the relay CF is released and the tube is conditioned ready to be fired on the next on period of the track circuit current and such operation will be repeated as long as" the track circuit is unoccupied. When the section D-E is occupied, the control voltage applied to the control grid I I is shunted and tube Vlremains non-conductive because of the negative bias voltage applied to the shield grid [2. g

It is to be seen, therefore, that as long as seetion DE is unoccupied, relay CF is operated at a rate corresponding to the code rate of the track circuit current and with relay CF operated to alternately close front contact 36 and back contact 3'! current impulses of a code rate corresponding to the code rate of the track circuit current are applied to a decoding unit shown conventionally at IBODU to energize a control relay AA. Decoding unit IEUDU may be of any one of the several constructions known to the art and is shown conventionally since its construction forms no part of my invention.

It is apparent that in Fig. 2 a loss of power at battery 26 so that there is a loss of bias voltage 1 for the shield grid results in a loss of power for the anode circuit. Also a broken circuit element of the shield grid circuit results in deenergizing check relay CC to interrupt the anode circuit. Thus in Fig. 2 the tube V! cannot be fired due to a loss of bias voltage.

Referring to Fig. 3, the track rails la and it are formed with a track section D-E provided with a track circuit supplied with coded direct current of the polar impulse code type. Code transmitter IBDCT of Fig. 3 is provided with a front contact 38 and a back contact 33 for governing a polar stick relay PS, the arrangement being such that when coder contact 38 is closed, a top winding of relay PS is energized to operate the armature of relay PS to the left to close polar contact 43 and when coder 6 contact 39 is closed, a lower winding of relay PS is supplied with current to operate the armature of that relay to the right to close polar contact 4 i. Thus when code transmitter IBUCT operates to close its front contact 38 there is a brief period before polar relay PS is operated to open its right-hand polar contact 4| and when code transmitter |CT is operated to close contact 39 there is a brief period before relay PS is operated to open its left-hand contact 40. During the brief period the coder is in position to close its contact 33 and the right-hand polar contact 41 of relay PS is closed, current is supplied to the track circuit from battery 42 current flowing r through contact 43 of the code transmitter, wire 44, rail la, the track relay or the train shunt if the section is occupied, rail lb, wire 45, and righthand polar contact 4! to battery 42; This impulse of current I shall consider as being of positive polarity. During the brief interval the code transmitter is in a position to close contact 39 and the polar contact 40 of relay PS is closed an impulse of current is supplied from battery 41, the circuit extending through contact 45 of the code transmitter, wire 44, rail la, track relay or train shunt to rail lb, wire 45, and polar contact 40 to battery 41. This code impulse of current I shall consider as being of negative polarity It follows that for each code cycle of the code transmitter two code impulses are supplied to the track circuit, the impulses being of opposite polarity and each of relatively short duration.

The track relay means for Fig. 3 includes two gas tubes V2 and V3 of any suitable type such as an indirectly heated tetrode. Each tube V2 and V3 is provided with two terminals for the shield grid in the manner explained in connection with tube VI of Figs. 1 and 2. The tubes V2 and V3 have their filaments heated in any convenient manner.

Each tube V2 and V3 is provided with a combined shield grid and anode circuit, such circuit for tube V2 extending from the positive terminal of a battery 48, through resistor 53, anode 60 and tube space to cathode 53 of tube V2, a bias resistor 55, one terminal to the other of shield grid 52 of tube V3, wire 5|, one terminal to the other of shield grid 50 of tube V2 and to battery 43. Similarly, the circuit for tube V3 extends from positive terminal of battery 48 through resistor 5t, anode BI and tube space to cathode 54 of tube V3, resistor 55, shield grid 52, Wire 5| and shield grid 56 to the negative terminal of battery 48.

It is to be seen that with either tube conductive the current flows through resistor 55 and creates a voltage drop which serves as a negative bias voltage for the shield grids of the tubes. In other words, the anode current of either tube serves to create a negative bias voltage for the other tube. If tube V2 is conductive the voltage drop across resistor 55 due to the anode current of tube V2 renders'shield grid 52 of tube V3 negative in potential with respect to cathode 54, and if tube V3 is conductive the voltage drop created across resistor 55 due to the anode current of tube V3 renders shield grid 50 of tube V2 negative in potential with respect to cathode 53. This voltage drop across resistor 55 is also applied to the shield grid of the conductive tube but is ineffective to control that tube due to the characteristics'of gas tubes. If tubes V2 and V3 are both conductive the voltage drop across resistor '55 is correspondingly increased but is ineffective 7 ti'onedthat battery 48 is of a voltagesuiilcient tov fire each tube were itnot for the bias voltage applied to the shield grid through resistor 55. It isto be. noted that with neither tube conductive there, is no bias voltage applied to the shield grids. In practicing the invention the tubes V2 and V3 would be arranged for one or the other of the tubes tobe initially conductive so that the shield grid of the other tube would be biased to maintain such other tube non-conductive until acontrol voltage is applied to such other tube in a manner to be explained shortly. As an alternative arrangement resistor 55 can be replaced by a battery.

A condenser C3 isconnected across the anodes of the tubes V2 and V3 and serves to alternately deionize the tubes in the well-known manner when the tubes are alternately fired through controlvoltages, alternately applied to the control grids of the tubes.

Resistor 69 is connected across the rails the sameas in Fig. 2, and a right-hand portion of resistor 69 is included in a control grid circuit for tube V2 and a left-hand portion of resistor V 69 is included in a control grid circuit for tube V3, as will be readily understood by an inspection of Fig. 3. 7 Thus, when the section D-E is unoccupied each code impulse of the track circuit current creates a corresponding voltage drop across resistor 69, the polarity being according to the polarity of the track circuit impulse.

In describing the operation of the apparatus of Fig. 3, I shall assume that at the start the tube V3 is conductivev and tube V2 is non-conductive, section D'--E is unoccupied and the first code impulse of the track circuit current is one that causes. the right-hand terminal of resistor 69 to be positive. Under such circumstances the control grid 62 of tube V2 is driven in the positive direction by the voltage drop across the right-hand portion of resistor 69. Thiscontrol voltagev Opposes the bias voltage of shield grid 50 of tube V2 and the parts are so proportioned that such control voltage permits tube V2 to be. fired. With both tubes V2 and V3 conductive, the charge of condenser C3 is applied across tor 59 caused by the conductive condition of tube V2, the right-hand terminal of condenser C3 being the positive terminal. The next code impulse of the track circuit current is of reverse polarity, and the voltage drop across resistor 69, causes. its left-hand terminal to be positive and a, control voltage is applied to control grid 64 of tube V3 to drive grid 66 in the positive direction in opposition to the bias of the shield grid 52. Such control voltage applied to tube V3 causes that tube to be fired. With both tubes conducting, the charge of condenser C3 is applied across the tubes and the polarity of the charge is such that tube V2 is deionized. Condenser C3is now recharged with its left-hand C3. now is applied to the tubes todeionizetube V3, and subsequent to thedeio izing of tube V3 the condenser C3 is rechargedwith its right-. hand terminal positive.

It is to be seen from the foregoing that the impulsesof the track circuit current alternately fire the tubes V2 and V3 and an electromotive force alternating in polarity at a rate corresponding to the code rate of the impulses of the track circuit current appears across the outside terminals of resistors 56 and 59. This electromotive force appearing across resistors 56 and 59 is applied to a decoding unit I8llDU tuned to effectively energize a control relay AA when the polarity of the electromotive force alternates at a frequency corresponding to the code rate of the track circuit current.

When the section D--E is occupied, the control voltage created across resistor '69 is shunted and the alternate operation of the tubes V2 and V3 ceases with one or the other of the tubes left conductive.

It is apparent that in Fig. 3 a loss of power that will cause a loss of the bias voltage, applied to the shield grids 5i] and 52 will also cause a loss of power to the anode circuit. broken connection in the combined shield grid and anode circuit of either tube V2 or V3 will open such anode circuit and the tubes cannot be fired.

It is to be understood that my invention is not limited to a shield grid as the control-elem trode of a tube to be provided with two terminals and included in series with a. bias voltage source and other tube electrodes can be used.

Although I have herein shown and described but three forms of railway track circuits embodying my invention, it is understood that various changes and modifications maybe made therein within the scope of the appended claims without departing from the spirit and scope of my iiivention.

Having thus described my invention, what I claim is:

1. In a track circuit the track rails of which are supplied with code impulses of direct cur-- rent alternate in polarity, a track relay means comprising; a first and a second gas tube each of "which has an anode, a cathode, a control grid and a shield grid; each said tube having two terminals which are connected one to each end of the shield grid of the same tube to in elude the shield grid inseries with its two terminals, a combined shield grid and anode circuit for each of said tubes and each of which circuits includes in series, a battery, the anode to cathode tube space of the respective tube, a bias. resistor and the two shield grids; said bias resistor and shield grids being common to the two shield gridanode circuits, each said shield grid circuit being disposed to provide a preselected shield grid bias voltage for the tube due to the voltage drop across said resistor, said battery of a voltage to fire the tubes but normally ineffective due to said bias voltage of the shield grid of each tube and which bias voltages are checked by said series connections of the shield grids and their terminals in the shield grid-anode circuits, circuit means connected across the control grid and cathodes of said first and second tubes, said circuit means including a resistor which is connected across said track circuit to receive said current impulses and which resistor is provided with terminals that are connected to said control grids and cathodes and poled to drive the control grid of said first tube positive in response Also, any

to current impulses of one polarity when they are applied to said circuit means and to drive the control grid of the second tube positive in response to current impulses of the other polarity when they are applied to said circuit means, means including a condenser connected across the anodes of said tubes and two other resistors one interposed in each of said shield grid-anode circuits to deicnize the tubes whereby said tubes are alternately fired in response to current irn pulses of alternate polarity applied to said circuit means, and means connected to said shield gridanode circuits of said tubes energized in response to such alternate firing of the tubes.

2. In a track circuit the track rails of which are supplied with impulses of current alternate in polarity, a track relay means comprising? a first and a second gas tube each of which has an anode, a cathode and a first and a second control electrode; each of said tubes having two terminals connected to the opposite ends of the second electrode of the tube, a source of direct voltage, a resistor; an anode-cathode circuit for each of said tubes and each of which circuits includes in series the positive terminal of said source, the anode to cathode tube space of the respective tube, said resistor, the second control electrode and its two terminals of each of the two tubes and the negative terminal of said source; said source of direct voltage being sufiicient to fire each tube, said resistor being of a value sufiicient for its voltage drop due to the conduction current of either tube to negatively bias the second control electrode of each tube suficiently to render the source of direct voltage ineffective to initially fire the tube, said negative bias being checked by the series arrangement of the anode-cathode circuits to include each second control electrode and its two terminals, another resistor connected across said track circuit to receive energy for current to fiow therethrough due to said impulses of current, control circuit means to connect one outside terminal and a mid terminal of said another resistor across the first control electrode and cathode of said first tube and to connect the other outside terminal and the mid terminal of said another resistor across the first control electrode and cathode of said second tube, and deionizing circuit means including a condenser connected across the anodes of the two tubes and two other resistors one interposed in each of the said anodecathode circuits adjacent the anode of the respective tube.

3. In a track circuit the combination comprising, a track section, means including a source of current connected across the rails of said section and operative to supply current impulses alternate in polarity; a track relay means including a first and a second gas tube each 01 which has an anode, a cathode and a first and a second grid; each said tube is provided with two terminals which are connected to opposite ends of the first grid the tube, source of power voltage, a source of bias voltage; an anodecathode circuit for each tube and each of which circuits includes in series said power source of voltage, the anode to cathode tube space of the respective tube, said source of bias voltage and the first grid and its two terminals of the respective tube; said source or power voltage being poled to render the anode of each tube positive in potential with respect to the cathode of the tube and being of a voltage sufficient to fire the tube, said bias voltage source being poled to render the first grid of each tube negative in potential with respect to the cathode of the tube and being of a voltage sufiicient to render said source of power voltage in effective to fire the tube, each said tube being provided with a check as to its nonccnductive condition due to said two terminals connected to the opposite ends of the first grid of the tube and due to said series arrangement of its anode-cathode circuit, circuit means including a resistor connected across the rails of section and having one outside terminal and a mid terminal connected across the second grid and cathode of said first tube and its other outside terminal and the mid terminal connected across the second grid and cathode of said second tube, the voltages applied to said second grids due to said track circuit current flowing in said resistor being effective to alternately overcome said bias voltages of said first grids and enable said power source of voltage to alternately fire the tubes, means including a condenser connected across the anodes or" the tubes to alternately deionize said tubes, and control means having an element common to said anode-cathode circuits energized by the conducticn currents of the tubes.

PAUL N. MARTIN.

REFERENCES CETED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,243,789 Wright Oct. 23, 1917 1,919,064 Hull July 18, 1933 2,221,653 Place Nov. 12, 1940 2,282,700 Chireix et al. May 12, 1942 2,297,119 Williamson et al. Sept. 29, 1942 2,354,024 Jerome July 18, 1944 2,439,680 Volz Apr. 13, 1948 FOREIGN PATENTS Number Country Date 586,080 Germany Oct. 16, 1933 

